In automotive vehicles, a radiator is provided in front of an engine, in order to cool cooling water warmed by the engine. The radiator is connected to the engine via a cooling water passageway so that the cooling water flows from the engine into the radiator. The radiator is cooled by air introduced thereinto from outside the vehicle, and thus, the temperature of the cooling water flowing within the radiator is also lowered. Various cooling apparatus for cooling engine cooling water have been proposed, one example of which is disclosed in Japanese Patent Publication No. SHO-63-46245 (JP S63-046245 B).
FIG. 5 is a view explanatory of a basic construction of the vehicle engine cooling apparatus disclosed in JP S63-46245 B. The cooling water warmed by the heat of the engine 101 is directed into the radiator 103 via the cooling water passageway 102. The cooling water thus directed into the radiator 103 is cooled, together with the radiator 103, by air taken in from outside an engine room as indicated by arrow (1). The thus-cooled cooling water is returned to the engine 101 via a cooling water discharge passageway 104 to thereby cool the engine 101.
In such a vehicle engine cooling apparatus, the engine 101 has not been warmed enough and the temperature of the cooling water is still low immediately after activation of the engine 101. Thus, the temperature of the cooling water need not be lowered until the engine 101 is warmed enough. Therefore, in such a case, a shutter 105 provided in front of the radiator 103 is closed to prevent air (indicated by arrow (1) in the figure) from contacting the radiator 103. Thus, the engine 101 is prevented from being cooled, so that the engine 101 can be warmed promptly after the activation. Once the temperature of the engine 101 exceeds a predetermined temperature and a need arises to lower the temperature of the cooling water, the shutter 105 is opened, and thus, the radiator 103 can be subjected to air taken in from outside the engine room so that the temperature of the cooling water can be lowered.
Sometimes, the vehicle is being run (or traveling) in a high-temperature environment for a long time. Under such a condition too, the cooling water for cooling the engine must be cooled sufficiently. For that purpose, a radiator core surface 106 is increased to allow the taken-in air to efficiently contact the radiator 103. Namely, the radiator core surface 106 is formed to have a great area so that it can sufficiently cool the cooling water even when the vehicle is being run in a high-temperature environment.
Because the radiator core surface 106 has a great area, the temperature of the cooling water tends to be rapidly cooled more than necessary if the vehicle is run with the shutter 105 kept opened under normal temperature. Once the cooling water drops below a predetermined temperature, the shutter 105 is closed, and thus, the temperature of the cooling water increases rapidly. Namely, with the vehicle engine cooling apparatus disclosed in JP S63-46245 B, the temperature of the cooling water frequently repeats increase and decrease and thus may become unstable. Stabilization of the cooling water temperature is desirable in that it can keep cooling the engine 101 in a stable manner.